Quantitative Aspects of Diffusion-weighted Magnetic Resonance Imaging in Rectal Cancer Response to Neoadjuvant Therapy

BACKGROUND The aim of the study was to evaluate the added value of the apparent diffusion coefficient (ADC) of diffusion-weighted magnetic resonance imaging (DW-MRI) in patients with rectal cancer who received neoadjuvant chemoradiotherapy (CRT). The use of DW-MRI for response evaluation in rectal cancer still remains a widely investigated issue, as the accurate detection of pathologic complete response (pCR) is critical in making therapeutic decisions. PATIENTS AND METHODS Thirty-three patients with locally advanced rectal cancer were evaluated retrospectively by MRI in addition to diffusion-weighted images (DWI) and its ADC pre- and post-neoadjuvant CRT. These patients subsequently underwent curative-intent surgery. Tumor staging by MRI and ADC value were compared with histopathological findings of the surgical specimen. RESULTS MRI in addition to DWI had a sensitivity of 96.1%, specificity of 71.4%, positive predictive value of 92.5%, and negative predictive value of 83.3% in the detection of pCR. The pre-CRT ADC alone could not reliably predict the pCR group. Post-CRT ADC cutoff value of 1.49 x 10-3 mm2/s had the highest accuracy and allowed a 16.7% increase in negative predictive value and 3.9% increase in sensitivity. Patients with pCR to neoadjuvant treatment differed from the other groups in their absolute values of post-CRT ADC (p < 0.01). CONCLUSIONS The use of post-CRT ADC increased the diagnostic performance of MRI in addition to DWI in predicting the final pathologic staging of rectal carcinoma.